Hibernate 实体映射

Question

大家晚安，

我想对具有以下实体及其透视关系的数据库建模：

但每次我运行 Java 项目在数据库中创建模型时，我创建的是这样的：

还有另一种映射这种关系的方法吗？我是这样映射的：

文章实体：

@Entity
public class Article {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private Boolean featured;

    @Column(nullable = false)
    private String title;

    @Column(nullable = false)
    private String url;

    @Column(name = "image_url", nullable = false)
    private String imageUrl;

    @Column(name = "news_site", nullable = false)
    private String newsSite;

    @Column(nullable = false)
    private String summary;

    @Column(name = "published_at", nullable = false)
    private String publishedAt;

    @OneToMany
    @JoinColumn(name = "launches_id")
    private List<Launches> launches;

    @OneToMany
    @JoinColumn(name = "events_id")
    private  List<Events> events;
}

启动实体

@Entity
public class Launches {
    @Id
    private String id;

    private String provider;
}

事件实体：

@Entity
public class Events {
    @Id
    private Long id;

    private String provider;
}

我想将此 JSON 映射到其他文章中出现的相同启动器和事件：

{
    "id": 4278,
    "title": "GAO warns of more JWST delays",
    "url": "https://spacenews.com/gao-warns-of-more-jwst-delays/",
    "imageUrl": "https://spacenews.com/wp-content/uploads/2019/08/jwst-assembled.jpg",
    "newsSite": "SpaceNews",
    "summary": "",
    "publishedAt": "2020-01-28T23:25:02.000Z",
    "updatedAt": "2021-05-18T13:46:00.284Z",
    "featured": false,
    "launches": [
        {
            "id": "d0fa4bb2-80ea-4808-af08-7785dde53bf6",
            "provider": "Launch Library 2"
        }
    ],
    "events": []
},
{
    "id": 4304,
    "title": "Government watchdog warns of another JWST launch delay",
    "url": "https://spaceflightnow.com/2020/01/30/government-watchdog-warns-of-another-jwst-launch-delay/",
    "imageUrl": "https://mk0spaceflightnoa02a.kinstacdn.com/wp-content/uploads/2020/01/48936479373_2d8a120c8e_k.jpg",
    "newsSite": "Spaceflight Now",
    "summary": "",
    "publishedAt": "2020-01-30T04:08:00.000Z",
    "updatedAt": "2021-05-18T13:46:01.640Z",
    "featured": false,
    "launches": [
        {
            "id": "d0fa4bb2-80ea-4808-af08-7785dde53bf6",
            "provider": "Launch Library 2"
        }
    ],
    "events": []
}

Answer 1

根据你的图表，应该是：

    @ManyToOne
    @JoinColumn(name = "launches_id")
    private Launches launches;

    @ManyToOne
    @JoinColumn(name = "events_id")
    private  Events events;

...而不是 @OneToMany ;)（可以有一个“文章”（id=x）具有 launchers_id=y AND launchers_id=z 吗？不，反之亦然！:)

...对于 @OneToMany，您应该在（关系的）“另一侧”找到连接列。

根据您的JSON，是OneToMany。但是，我们必须 draw/expect:

@Entity
class Article {
    //... id, columns, blah
    @OneToMany
    @JoinColumn(name = "article_id")  // Launches "owns the relationship"/column 
    private List<Launches> launches;

    @OneToMany
    @JoinColumn(name = "article_id")  // Events...!
    private  List<Events> events;
}

通常，（当您通过 json 公开您的数据库模型时）确保：

没有“圈子”（在双向关联中）。 (@JsonManagedReference, @JsonBackReference, @JsonIgnoreProperties, ... )
不公开您不想公开的数据。 (@JsonIgnoreProperties, ...)

关于Hibernate-ManyToOne，请参考https://vladmihalcea.com/the-best-way-to-map-a-onetomany-association-with-jpa-and-hibernate/

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Hibernate 实体映射

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